Errors in saving non-standard element types

Consider the following code:

julia> df = DataFrame(x = [',','\n', ','])
3×1 DataFrame
│ Row │ x    │
│     │ Char │
├─────┼──────┤
│ 1   │ ','  │
│ 2   │ '\n' │
│ 3   │ ','  │

julia> df |> save("test.csv")

julia> println(read("test.csv", String))
"x"
,


,


julia>

And the saved file is broken because non-strings are saved as not quoted.

Here is an extreme example (not to say it happens in reality, but just shows that it could be handled better). The code is a continuation of the earlier code:

julia> DataFrame(d=[df, df]) |> save("test2.csv")

julia> println(read("test2.csv", String))
"d"
3×1 DataFrame
│ Row │ x    │
│     │ Char │
├─────┼──────┤
│ 1   │ ','  │
│ 2   │ '\n' │
│ 3   │ ','  │
3×1 DataFrame
│ Row │ x    │
│     │ Char │
├─────┼──────┤
│ 1   │ ','  │
│ 2   │ '\n' │
│ 3   │ ','  │

and it is completely unreadable back (even as string) because it is not quoted again.

Finally let us consider a more normal scenario, which is again broken because of non-quoting:

julia> df = DataFrame(a=Date("2000-10-10"), b=Date("2000-11-11"))
1×2 DataFrame
│ Row │ a          │ b          │
│     │ Date       │ Date       │
├─────┼────────────┼────────────┤
│ 1   │ 2000-10-10 │ 2000-11-11 │

julia> df |> save("test3.csv", delim="-")

julia> println(read("test3.csv", String))
"a"-"b"
2000-10-10-2000-11-11

@davidanthoff Not sure which of the issues above can be fixed but at least I wanted you to be aware of them.

Start by reproducing the three examples using save("test.csv"), save("test2.csv"), and save("test3.csv", delim="-"). Trace the save path for non-string values and check how delimiters, newlines, and nested displayed values are handled. Done means the resulting CSV remains readable when values contain delimiters or newlines and the reported examples no longer produce broken rows.